Using memory address as ThreadID sometimes gives different threads the same address

In my program, I've created 3 threads and then added them all to a controller thread. However, one thread was never executed (I had print-statements that should have run) and after some debugging I noticed that the size of the controller thread showed 2, when it should have been 3. I did not use thread names. I am only using lambda functions as callback functions for the threads.

Looking at the thread-controllers add function, I saw that a thread is not added when the controller already has a thread with the same ID. I printed the thread-ids of all my threads and it turned out that the 1st and the 3rd thread got the same ID, so the 3rd thread was never added. But this should not be possible as different threads should get different ids?

When I added Serial.println() before and Serial.println(controller.size()) after adding the 3rd thread to the controller, all 3 threads got different IDs. I can not explain this behaviour.

Thus, my conclusion is that using memory address as ThreadID feels unpredictable. Maybe thread id could be substituted by a random number instead? (I did this as a workaround).

Start with the thread-controllers add function and the ThreadID generation that uses memory addresses. Reproduce the case with three lambda-based threads, comparing their IDs and the controller size with and without Serial.println() calls. Done means distinct threads are retained and the controller reports all three consistently.

Written by the indexing model from the issue text.